Sustained groundwater level changes and permeability variation in a fault zone following the 12 May 2008, M_w 7.9 Wenchuan earthquake

摘要

We analyse the groundwater level changes following the Wenchuan earthquake in three wells - NX, DZ and BBLY - located in the same fault zone, in the near field (distance of similar to 300km from the epicentre). Co-seismic falls in the water level and gradual recovery were recorded in these wells but with different recovery periods (from 200days to more than 1600days). The response of the groundwater level to Earth tides is used as a proxy to explore the permeability evolution. We found that the permeability increased in response to the Wenchuan earthquake in the three wells but with different post-earthquake recovery processes. Only BBLY recovered to its pre-earthquake value 260days after the Wenchuan earthquake and remained stable. The permeability in NX returned to its pre-earthquake value over a similar period but then continued to drop. The permeability in DZ returned to its pre-earthquake value much quicker than that in the other two wells and remained stable below the pre-earthquake value 200days after the earthquake. This suggests that the groundwater level changes in the three wells were mainly caused by permeability changes. In the BBLY well, the unclogging/clogging of the fracture flow path mechanism may explain the permeability evolution, whereas mechanisms such as unclogging/clogging or the opening/closing of the fracture associated with blocking of the narrow fracture apertures appears to be responsible for the permeability evolution in the NX and DZ wells. Copyright (c) 2014 John Wiley & Sons, Ltd.